A K-9 police unit walks through the crime scene where an off-duty Philadelphia police officer was shot and killed Saturday in North Philadelphia. Police said the officer had just gotten off his overnight shift and was not wearing his uniform as he walked along Cecil B. Moore Avenue, where he was shot multiple times just before 6 a.m., Saturday. The officer later died at the hospital. (ASSOCIATED PRESS / Joseph Kaczmarek)

PHILADELPHIA (AP) — A police officer was shot to death blocks from his precinct house just after he finished his shift early Saturday in what authorities suspect was a street robbery. Police announced rewards totaling $30,000 to help them make an arrest.

Officer Moses Walker Jr., 40, was shot several times around 6 a.m. about four blocks from his station in north Philadelphia, police said. He wasn't wearing a uniform. The 19-year-veteran, who was unmarried and had no children, was pronounced dead at a hospital in a city where on average nearly one person has been slain every day this year.

Commissioner Charles Ramsey said Walker's death is a blow for a department still mourning the loss of Highway Patrol motorcycle officer Brian Lorenzo, who was killed last month in a wrong-way crash on Interstate 95.

"This department has been through an awful lot," he said. "In just the 4½ years that I've been here, this would be the seventh officer we've lost, which is more than some departments get in 20 years."

Lt. Raymond Evers said Walker's service weapon was found under his body, but police don't know whether it was fired. Investigators were also trying to determine if anything was taken from the officer's backpack. While detectives hadn't ruled anything out, "we're more leaning toward a street robbery" as the reason for the slaying, Evers said.

Police were asking for information from anyone who may have seen someone running from the scene and were seeking any footage from security cameras facing the street in the area.

The city is offering a $20,000 reward and the Fraternal Order of Police Lodge 5 is offering a $10,000 reward, police said. Mayor Michael Nutter ordered all city flags flown at half-staff in the officer's honor.

From 2006 to 2009, eight officers died in the line of duty from either gunfire or vehicular assault. Two of the four officers killed in 2008 died when stolen vehicles rammed their cruisers.

The general homicide rate in Philadelphia has risen sharply in recent years. After falling to just over 300 a year in 2009 and 2010, the City of Brotherly Love recorded a total of 324 homicides last year and is reporting just under one homicide every day so far this year.

In the hours before the officer was shot, three men were killed by gunfire and a number of other people wounded, some critically, in other shootings and stabbings around the city.

Evers said the officer slayings in recent years occurred during myriad circumstances: several vehicle crashes, a foot chase and car chase, and a number of shootings, some occurring when officers responded to or walked in on crimes.

The overwhelming factor, however, was "too many guns out there," particularly illegal ones, he said.

"When we catch this guy, I guarantee you he's not going to be an upstanding citizen with a license to carry," Evers said. "He's going to be a bad guy with a long record with an illegal gun."

Nutter cited the three other overnight deaths in calling on residents to help crack down on the city's firearms carnage.

"We will not make headway in dramatically reducing the scourge of gun violence and the proliferation of illegal guns until we as a community stand together and offer all information that we have on the perpetrators of violence in our city," he said in a statement.